1,2,3,5,6-Pentathiepane (hereinafter, sometimes referred to as “lenthionine”) is a compound useful for optical material applications (Patent document 1) and medical applications (Patent document 2), which is expected to be used for a wide range of applications.
As a method for synthesizing lenthionine, for example, a method that uses dimethyl disulfide as a starting raw material is known (Non-patent document 1). According to this method, the reaction results an oily solution that contains lenthionine and thus it needs to be purified by column chromatography, which is industrially disadvantageous. Moreover, dimethyl disulfide that is uneasy to obtain for industrial application needs to be used as the raw material.
Meanwhile, a method is known in which sodium sulfide as a starting raw material is allowed to react with diiodomethane or dibromomethane in an ethanol solvent (Non-patent document 2). This method also requires column chromatography for purification, which is industrially disadvantageous.
In general, disulfide and trisulfide are known to be susceptible to linkage and cleavage. Since lenthionine has disulfide and trisulfide bonds, polymerization proceeds when these bonds are cleaved, resulting an insoluble polysulfide compound.
Generation of a large amount of the insoluble polysulfide compound in the reaction system not only makes washing and industrialization difficult, but eventually makes acquirement of highly pure lenthionine difficult due to contamination in the final lenthionine. Generation of this polysulfide is making purification in the known lenthionine syntheses difficult.